MECHANISM OF THE HIPPOCAMPAL LOSS OF ADENOSINE SENSITIVITY IN CALCIUM-FREE MEDIA

Adenosine depresses the excitability of pyramidal neurones in the hipp ocampus. This effect is lost in calcium-free media and we have now inv estigated the mechanism of this. Extracellular recordings were made of antidromically and orthodromically evoked population potentials from CA1 region of rat hippocampal slices. It was observed that the activit y of adenosine can be restored in the presence of procaine or carbamaz epine, known inhibitors of sodium channels. The GABA(B) agonist baclof en was able to depress potential size but did not restore sensitivity to adenosine. It is concluded that the loss of postsynaptic sensitivit y to adenosine in calcium-free solution results from the increased sod ium conductances.